Farms, vegetable processing plants, meat processing plants, creameries and cheese processing plants, and restaurants have continually struggled with the disposal of organic waste. For example, pig farms produce tremendous amounts of pig manure. This manure has become the object of public controversy because of environmental concerns such as run-off pollution and odor.
Traditionally, organic waste is disposed of by using it as fertilizer in a farming operation. However, environmental regulations now restrict the time of the year and weather conditions during which manure, especially liquefied manure, can be spread; and, in some cases, require the manure to be plowed in immediately which is not always possible. This requires the farmer to invest in costly manure storage units or to pay to have the manure removed. Regulations also restricts the amount of nutrients, particularly phosphorus, that can be applied in a given area of land, requiring farmers to either purchase more land or to pay other land owners to spread the excess manure.
Anaerobic digestion is another method of disposing of manure containing high concentrations of organic matter. Through anaerobic digestion, large quantities of organic matter are broken down by bacteria that convert the organic matter into biogas. Anaerobic digestion is particularly suitable for disposing of liquefied manure containing high concentrations of organics. In addition, operators can also use or sell the biogas that is produced. In digested manure, nutrients are broken-down. Consequently, plants can absorb digested manure faster, thereby requiring less land to spread a given amount of manure.
Traditional anaerobic digesters suffer from plugging where heavy and light solids that precipitate from the organic waste coalesce into obstructions that prevent the flow of the effluent produced during digestion. The plugging occurs frequently and becomes a nuisance for the operator. Consequently, the operator (farmer, owner, etc.) devotes a considerable amount of time towards maintaining the anaerobic digester. Plugging of the digester interrupts the steady flow of the digestion process disturbing and slowing down the bacterial activity. Additionally, unplugging a digester risks the removal of the mass of bacteria that digest the organic material. If the bacteria population is diminished, it will take days before the bacteria repopulates to an optimal level. Complicating matters, increasing the rate of anaerobic digestion increases the amount of organic waste processed, which increases the frequency and severity of plugging.
Furthermore, traditional anaerobic digesters are typically semi-permanent installations and cannot be moved easily. To move a digester, a team would need to prepare a new site, disassemble the digester, and move the individual pieces to the new site. Then, an engineering team would reassemble the digester piece-by-piece. Consequently, it is expensive to move a digester. Thus, operations that are interested in using a digester only for a short time will be dissuaded from doing so.
For example, a crop processing plant produces a tremendous amount of waste during the harvest; hence, the need for a digester is great. However, during the growing season the need for digesters is diminished. Despite the periodic need, the crop processing plant does not invest in a permanent installation because of the capital requirements.
Therefore, there is a need for a high rate anaerobic digester that is portable, automated, and plugs infrequently.